This invention relates generally to a method of treating organic material to create a fertilizer. More specifically, the invention relates to the treatment of organic material, such as sewage sludge, with an acid and base in a pipe-cross reactor.
The disposal of sewage sludge is a problem. Current methods of disposing of sewage sludge include incineration, direct land or ocean application, heating and drying the sludge for sterilization and then applying it to the land, depositing it in a landfill, or granulating it with a standard rotary granulator, with heating and drying being provided by exogenous heat sources (e.g. by burning purchased fuel). While some of these methods result in what is termed a xe2x80x9cfertilizerxe2x80x9d, such fertilizer is of relatively low analysis with regard to its xe2x80x9cplant nutrient valuexe2x80x9d.
Methods of expressing a fertilizer""s xe2x80x9cplant nutrient valuexe2x80x9d involve identifying the fertilizer""s xe2x80x9cNPKxe2x80x9d value, wherein N relates to the amount of nitrogen, P relates to the amount of phosphorus (expressed as P2O5), and K relates to the amount of potassium (expressed as K2O). Thus, as reported by Wilson in U.S. Pat. No. 3,050,383 (Aug. 21, 1962), sewage sludge with a 2.5-2.5-0value contains two and a half percent nitrogen, two and a half percent phosphorous as P2O5, and zero percent potassium as K20. Except as otherwise indicated by usage, all percentage values used herein are weight-based percentages (i.e., w/w).
Fortunately, methods exist for enhancing the nutrient value of relatively low analysis organic waste material. For instance, in the aforementioned Wilson patent (the contents of the entirety of which are incorporated by this reference), a method is disclosed for treating dried animal manure and sewage sludge with controlled amounts of an acid, such as sulfuric acid, phosphoric acid (or an equivalent phosphorous compound, the strength of which is expressed as phosphoric acid), or mixtures thereof, and an aqueous ammoniacal solution, such as aqueous ammonia or ammoniacal nitrogen salt-containing solutions and tumbling the resulting reaction mass to form fertilizer granules having an xe2x80x9cupgradedxe2x80x9d or xe2x80x9cenhancedxe2x80x9d plant nutrient value.
Other methods of enhancing the plant nutrient value of relatively low analysis organic waste material with acids, bases, or mixtures thereof have also been described. See, e.g., U.S. Pat. No. 4,743,287 (May 10, 1988) to Robinson, U.S. Defensive Publication T955,002 (Feb. 1, 1977) to Norton et al., U.S. Pat. No. 5,466,273 (Nov. 14, 1995) to Connell, U.S. Pat. No. 5,125,951 (June 30, 1992) to Lahoda et al., U.S. Pat. No. 5,118,337 (Jun. 2, 1992) to Bleeker, U.S. Pat. No. 5,393,317 (Feb. 28, 1995) to Robinson, and U.S. Pat. No. 5,422,015 (Jun. 6, 1995) to Angell et al.
A further drawback of sludges treated in conventional manners (e.g., by drying and screening) is that they are usually of insufficient size and shape to be spread by commonly used agricultural fertilizer spreaders, and cannot be used in the newer pneumatic spreaders.
It would be an improvement in the art if a relatively simple process existed for processing relatively low analysis organic waste material to an enhanced plant nutrient value composition, especially if such a process yielded a product which was sized and shaped to be spread by presently commercially available spreaders.
The invention includes an improved process for enhancing the plant nutrient value of relatively low analysis organic waste material, such as sewage sludge. The improvement involves exothermically treating the relatively low analysis organic waste material with an acid and a base in a pipe-cross reactor.
More particularly, the improved process involves mixing the relatively low analysis organic waste material with water to form a slurry (or taking the waste material as a slurry); pumping the slurry to a pipe-cross reactor for reaction with a base, acid, and water to form a melt; spraying the melt onto a recycling bed of fines, and flashing off the water contained in the melt as steam. The melt is then rolled onto a substrate such as recycled fine particles in a granulator to form granulated particles, causing the granulated particles to grow in size (e.g., to form granules). These granulated particles are then dried (e.g., with a rotary dryer) to reduce their moisture content, and form an enhanced plant nutrient value composition (e.g., a fertilizer or soil conditioner having a greater NPK value than the original relatively low analysis organic waste material).
Generally, the process will also include passing the dried granulated particles to a separation apparatus and separating the dried granulated material into fines, product, and oversized material, and further includes grinding the oversized material and returning the fines and oversized material to the granulator for use as a granular substrate. Potash and other micronutrient materials may be added as dry material to the returning fines for further enhancement of the product.
The invention also includes fertilizer produced according to the improved process. Fertilizers produced by the instant invention are of the same size and shape and density of commonly used fertilizers.
An advantage of the method is that it uses the heat generated by the exothermic acid-base reaction in the pipe-cross reactor to remove the approximately 80% water from sludge, thus saving large amounts of energy normally used in conventional drying or burning methods, while, at the same time, conserving the intrinsic values of the nutrients and humates contained in the sludge. The method also handles the processed material as a slurry, thus avoiding the nuisance of conveying and handling dry or solid materials. The method also achieves high temperatures which aids in the destruction of pathogens.
In one embodiment, the process includes a method of disposing of spent acid from a hot dip galvanizing process or a steel pickling process comprising incorporating the spent acid to maintain the low pH of a venturi scrubber used in the improved process thus producing a micronutrient enriched fertilizer.